The present invention is related to polishing of materials, in particular to the chemical mechanical polishing (CMP) of integrated circuits. Specifically, a method for placing a transparent section in a polishing pad is described. In particular, the present invention is directed to forming or placing an end-point-detecting, laser-transparent window in a CMP polishing pad disclosed in above-mentioned parent application Ser. No. 10/349,201, or the porous polishing pad disclosed in commonly-owned U.S. patent application Ser. No. 10/087,223, filed on Mar. 1, 2002, which applications are incorporated by reference herein. The CMP porous polishing pads disclosed therein are made of a matrix of porous paper-making fibers that is impregnated and bound together with a thermoset resin. Such a polishing pad is a matrix of absorbent cellulose fibers, for example, and are impregnated with a thermoset resin, preferably phenolic, is densified, and cured to provide a rigid, yet porous structure. The porous CMP polishing pads thereof are made by a wet-laid, specialty paper-making process.
In the field of semiconductor manufacture, numerous integrated circuits are produced on wafers through layers of wiring devices. During the process of forming layers and structures, the topography of the surface becomes increasingly irregular. The prevailing technology for planarizing the surface is chemical mechanical polishing (CMP). In effect, this process polishes the top layer of an integrated circuit prior to the depositing of another layer.
In most chemical-mechanical polishing, the working layer of an integrated circuit is exposed to a moving polishing pad and a chemical slurry solution. In some systems, the polishing pad, mounted on a platen, rotates about a fixed axis, while the wafer rotates and moves across the pad. Since material on the active layer is removed during the process, it is critical that the polishing process be terminated at the correct time. In order to control the end point of the polishing process, various methods have been developed. The most prevalent method has utilized laser interferometry which detects the end point of the polishing process, an example of which is disclosed in U.S. Pat. No. 6,280,289.—Wiswesser, et al. In these systems, a laser is mounted in the platen and directed through the pad onto the surface of the wafer. A control system detects changes in the reflected signal to determine the end point.
In order for end-point detection to be carried out, the pad must have a section that is reasonably transparent to the wavelength of the laser being used. Most methods for producing a transparent region in the polishing pad involve inserting a formed, transparent plug into a hole in the pad. The plug is usually secured to the pad by an adhesive film onto the back, or rear, non-working side or surface of the polishing pad.